1. Field of the Invention
This invention relates to a rotary-type electromagnetic actuator applicable to the steering of a toy automobile, the opening and closing of a hand of a toy robot, the blinking of an eye of a doll, etc. More particularly, the invention relates to a rotary-type electromagnetic actuator which makes possible back-and-forth rotational motion through an angle of 360.degree. or less by the energization of a coil, and wherein brushes for supplying the coil on the rotor side with electric current also function to adjust a home position to which the rotor is returned.
2. Description of the Prior Art
FIGS. 5 and 6 illustrate an example of a conventional rotary-type electromagnetic actuator adapted to steer a radio-controlled toy automobile. As shown in FIGS. 5 and 6, the conventional electromagnetic actuator includes a generally box-shaped actuator receptacle 1 molded as an integral part of a synthetic resin chassis 1a and having its upper side open, a cylindrical stator 2 comprising a magnet securely mounted within the receptacle 1, and a generally I-shaped rotor 3 arranged within the stator 2 in concentric relation therewith. A shaft 4 fixedly penetrates the rotor 3 at its center and has both its ends rotatably supported by bearings 5a, 5b formed in respective openings located in the upper edge of the receptacle 1. A coil 6 is wound on an end portion of the rotor 3 and is adapted to be supplied with dc power (+), (-) through flexible lead wires 6a6b connected to respective ends of the coil. A forward or reverse torque is produced in the rotor 3 by changing the polarity of the DC power suppled to the coil 6. A cover 7 made of synthetic resin is affixed to the edge of the open upper side of receptacle 1 by an adhesive or other suitable means to cover the upper side of the stator 2. One side of the cover 7 is formed to include an aperture 8 through which the lead wires 6a, 6b of coil 6 may be led out from the receptacle 1. Stoppers 9a, 9b for limiting the angle of rotation of the rotor 3 in the forward and reverse directions are secured to the inner wall surface of the stator 2.
When the coil 6 of this rotary-type electromagnetic actuator having the above-described construction is not being supplied with current and, hence, is in the deenergized state, both ends of the rotor 3 are attracted to the N and S magnetized portions of the stator 2 so that the position of the rotor 3 is maintained, as shown in FIG. 6. If the dc power is now supplied to the coil 6 with the polarity shown in FIG. 6, the rotor 3 will rotate in the direction of arrow A in FIG. 6 until it strikes the stopper 9a, at which angular position the rotor 3 will be held. The resulting rotational torque is transmitted from the shaft 4 to the front wheels (not shown) of the toy automobile through a linkage mechanism (not shown), so that the front wheels will be steered to the right (or left) side.
If the dc current supplied to the coil 6 has a polarity which is the opposite of that shown in FIG. 6, the rotor 3 will rotate in a direction opposite that of arrow A until it strikes the stopper 9b, at which angular position the rotor 3 will be maintained. If the current supplied to coil 6 is cut off, the rotor 3 will be returned to the home position shown in FIG. 6 by the magnetic force of the stator 2.
When the rotor 3 in this conventional actuator rotates back and forth in the manner described, the lead wires 6a, 6b of the coil 6 swing back and forth in the direction of the rotor 3. As a result, flexure stress concentrates at the portions where the coil 6 and lead wires 6a, 6b are soldered together. In consequence, these portions tend to break, causing the actuator to malfunction. Another problem with the conventional arrangement is that a spring force possessed by the lead wires 6a, 6b inhibits the motion of the rotor 3 and does not allow the rotor 3 to return to its home position in a stable manner. Consequently, when this electromagnetic actuator is mounted on, say, the chassis of a toy automobile and the rotor shaft 4 is connected to the front-wheel steering linkage mechanism in order for the actuator to be used to steer the toy automobile, there is no assurance that the front wheels will always be aligned straight ahead when the coil 6 is in the deenergized state. This can impede the performance of a radio-controlled toy automobile in a race and detract from the steerability of the toy automobile. Moreover, if machining or assembly errors exist in the front-wheel steering linkage mechanism or there is an error in the mounting of the electromagnetic actuator on the toy chassis or a machining error in the receptacle 1, this will directly affect the straight-ahead attitude of the front wheels relative to the home position of the rotor 3. As a result, the front wheels will be offset to the left or right and will not be maintainable in the straight-ahead attitude. Correcting this offset of the front wheels is a troublesome and time-consuming task.
Further, in order for the movement of the lead wires 6a, 6b that swing with the back-and-forth rotational motion of the rotor 3 not to be impeded, the aperture 8 through which these wires are passed must be made large in size. When this is done, however, sand, dust and other contaminants readily penetrate the interior of the receptacle and can cause the actuator to develop a variety of problems. In addition, since the receptacle 1 is molded as an integral part of the chassis, use of the electromagnetic actuator installed withn the receptacle is restricted to the toy automobile exclusively, so that the actuator cannot be used for some other purpose. A problem that results is higher cost.